GRAIN BOUNDARY- AND SURFACE-DOPED LITHIUM-LANTHANUM-ZIRCONIUM COMPOSITE OXIDE ELECTROLYTE, PREPARATION METHOD THEREFOR, AND APPLICATION THEREOF

Abstract

Disclosed are a grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte, a preparation method therefor, and an application thereof. Part of doping elements are step-doped at the grain boundary and the surface of the lithium-lanthanum-zirconium composite oxide solid electrolyte to improve the distribution state of the doping elements at the grain boundaries, reduce the number of grain boundaries, lower the grain boundary resistance of the lithium-lanthanum-zirconium composite oxide, thereby obtaining high ionic conductivity. The doping method has the advantages of being simple and convenient in process, low in cost and high in universality, can meet the requirements of different solid electrolytes on doping elements, and is suitable for large-scale application. The solid electrolyte obtained from the technical solution of the present application can be used in fields such as all-solid-state lithium or lithium ion batteries, semi-solid lithium ion batteries, lithium air batteries and the like.

Claims

1. A grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte, wherein, the chemical formula of the solid electrolyte is Li.sub.7-xLa.sub.3-yZr.sub.2-zM.sub.O.sub.12-D.sub.; wherein M comprises one or more cationic doping elements and D comprises one or more anionic doping elements, and 0x3, 0y1.5, 0z1, 0<<3, 01.5, and 01.

2. The grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to claim 1, wherein, the solid electrolyte contains an oxide of Li and M, or one or more of the oxide of Li and M and a fluoride, sulfide, nitrogen-containing compound, phosphate, and complex thereof formed from Li, M, and D at the grain boundary and the surface thereof.

3. The grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to claim 1, wherein, the doping element M comprises one or a combination of more than one of cations Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, B, Al, Ga, In, Si, Ge, Sn, Sb, Bi, Se, Te, Nb, Mo, Hf, Ta, W, and rare earth elements other than La; preferably, the doping element M comprises one or a combination of more than one of cations Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, In, Ge, Sn, Sb, Te, Nb, Mo, Ta, Ce, Pr, Nd, Sm, Eu, Gd, Yb, Sc, and Y; further preferably, the doping element M comprises one or a combination of more than one of cations Mn, Fe, Co, Ni, Al, Ga, Nb, Ta, Ce, Pr, Nd, Sm, Gd, Yb, and Y; and the doping element D comprises one or a combination of more than one of anions N, F, P, and S.

4. The grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to claim 1, wherein, the molar content of the doping element M is less than or equal to 12% of the molar amount of the solid electrolyte by mole; and the molar content of doping element D is less than or equal to 5% of the molar amount of the solid electrolyte.

5. The grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to claim 1, wherein, the lithium-lanthanum-zirconium composite oxide comprises a garnet-type structure.

6. A preparation method for the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to claim 1, comprising the following steps: S1, mixing aqueous solutions of lanthanum and zirconium compounds in a desired stoichiometric ratio to obtain a mixed material liquid; adding the mixed material liquid and an alkaline substance into a reactor for a precipitation reaction; performing suction filtration, washing, drying, and roasting on the obtained precipitate to obtain a lanthanum-zirconium oxide; and S2, mixing the lanthanum-zirconium oxide with liquid salts of doping elements M and Li under a stirring condition in one or more steps, drying and then performing once or twice heat treatments, and then performing once or twice calcinations to obtain the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte; wherein the zirconium source in the mixed material liquid in step S1 comprises one or a combination of more than one of zirconium oxychloride, zirconium oxynitrate, zirconium sulfate, zirconium acetate, and zirconium citrate; the lanthanum source comprises one or a combination of more than one of lanthanum chloride, lanthanum nitrate, lanthanum sulfate, lanthanum acetate, and lanthanum citrate.

7. The method according to claim 6, wherein, all or part of Li in the form of solid salt is added to the M-containing lanthanum-zirconium oxide.

8. The method according to claim 6, wherein, the alkaline substance comprises magnesium bicarbonate, urea, and at least one of hydroxide, carbonate, or bicarbonate of at least one element of ammonium, sodium, or potassium, preferably comprises at least one of sodium hydroxide, urea, aqueous ammonia, and ammonium bicarbonate.

9. The method according to claim 6, wherein, in step S1, adding the mixed material liquid and the alkaline substance into the reactor for the precipitation reaction, the pH during the precipitation process is controlled in the range of 4.5-14, preferably 5-10; the endpoint pH of the precipitation is controlled at 8-13, preferably 9-11; the temperature is controlled at 0-120 C., preferably 10-80 C.; and the roasting temperature in step S1 is 600-1000 C., preferably 700-900 C.; and the roasting time is 1-24 h, preferably 3-15 h.

10. The method according to claim 6, wherein, the liquid salt of the doping element M or Li comprise one or a combination of more than one of nitrate, acetate, sulfate, citrate, and an amino acid salt molten salt or aqueous solution.

11. The method according to claim 6, wherein, doping element D is added in one or more of the steps S1 and S2; the doping element D is derived from one or a combination of more than one of nitrate, fluoride, phosphate, sulfate, and sulfide.

12. The method according to claim 6, wherein, the heat treatment temperature in step S2 is 200-750 C., preferably 400-600 C.; and the heat treatment time is 1-24 h, preferably 3-15 h; and the calcination temperature in step S2 is 700-1100 C., preferably 800-950 C.; and the calcination time is 1-24 h, preferably 3-15 h.

13. A preparation method for the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to claim 1, comprising the following steps: S1, mixing aqueous solutions of lanthanum and zirconium, and M or a part of M compound in a desired stoichiometric ratio to obtain a mixed material liquid; adding the mixed material liquid and an alkaline substance into a reactor for a precipitation reaction; performing suction filtration, washing, drying, and roasting on the obtained precipitate to obtain an M-containing lanthanum-zirconium oxide; and S2, mixing the M-containing lanthanum-zirconium oxide with a liquid salt of Li or a mixed liquid salt of the remaining doping element M and Li under a stirring condition in one or more steps, drying and then performing once or twice heat treatments, and then performing once or twice calcinations to obtain the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte; wherein the zirconium source in the mixed material liquid in step S1 comprises one or a combination of more than one of zirconium oxychloride, zirconium oxynitrate, zirconium sulfate, zirconium acetate, and zirconium citrate; the lanthanum source comprises one or a combination of more than one of lanthanum chloride, lanthanum nitrate, lanthanum sulfate, lanthanum acetate, and lanthanum citrate.

14. The method according to claim 13 wherein, all or part of Li in the form of solid salt is added to the M-containing lanthanum-zirconium oxide.

15. The method according to claim 13, wherein, the alkaline substance comprises magnesium bicarbonate, urea, and at least one of hydroxide, carbonate, or bicarbonate of at least one element of ammonium, sodium, or potassium, preferably comprises at least one of sodium hydroxide, urea, aqueous ammonia, and ammonium bicarbonate.

16. The method according to claim 13, wherein, in step S1, adding the mixed material liquid and the alkaline substance into the reactor for the precipitation reaction, the pH during the precipitation process is controlled in the range of 4.5-14, preferably 5-10; the endpoint pH of the precipitation is controlled at 8-13, preferably 9-11; the temperature is controlled at 0-120 C., preferably 10-80 C.; and the roasting temperature in step S1 is 600-1000 C., preferably 700-900 C.; and the roasting time is 1-24 h, preferably 3-15 h.

17. The method according to claim 13, wherein, the liquid salt of the doping element M or Li comprise one or a combination of more than one of nitrate, acetate, sulfate, citrate, and an amino acid salt molten salt or aqueous solution.

18. The method according to claim 13, wherein, doping element D is added in one or more of the steps S1 and S2; the doping element D is derived from one or a combination of more than one of nitrate, fluoride, phosphate, sulfate, and sulfide.

19. The method according to claim 13, wherein, the heat treatment temperature in step S2 is 200-750 C., preferably 400-600 C.; and the heat treatment time is 1-24 h, preferably 3-15 h; and the calcination temperature in step S2 is 700-1100 C., preferably 800-950 C.; and the calcination time is 1-24 h, preferably 3-15 h.

20. Use of the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to claim 1 in all-solid lithium metal or lithium ion batteries, semi-solid lithium ion batteries, lithium air batteries.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a flow chart of a preparation method for a grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to the present application.

DETAILED DESCRIPTION OF THE APPLICATIONS

[0034] In order to make the purpose, technical solution, and advantages of the present application clearer, the following is a detailed explanation of the present application, combined with specific embodiments and referring to the accompanying drawings. It is to be understood that this description is made only by way of example and not as a limitation on the scope of the present application. Further, in the following description, descriptions of publicly known structures and techniques are omitted to avoid unnecessarily confusing the concepts of the present application.

[0035] In a first aspect of the present application, provided is a grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte. The chemical formula of the solid electrolyte is Li.sub.7-xLa.sub.3-yZr.sub.2-zM.sub.O.sub.12-D.sub.; wherein M includes one or more cationic doping elements and D includes one or more anionic doping elements; and 0x3, 0y1.5, 0z1, 0<<3, 0 1.5, and 01. The solid electrolyte contains an oxide of Li and M, or one or more of the oxide of Li and M and a fluoride, sulfide, nitrogen-containing compound, phosphate, and complex thereof formed from Li, M, and D at the grain boundary and the surface thereof, effectively reducing the grain boundary resistance of the lithium-lanthanum-zirconium composite oxide, thereby effectively improving the ionic conductivity thereof.

[0036] The doping element M may include one or a combination of more than one of cations Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, B, Al, Ga, In, Si, Ge, Sn, Sb, Bi, Se, Te, Nb, Mo, Hf, Ta, W, and rare earth elements other than La; preferably, the doping element M includes one or a combination of more than one of cations Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, In, Ge, Sn, Sb, Te, Nb, Mo, Ta, Ce, Pr, Nd, Sm, Eu, Gd, Yb, Sc, and Y; further preferably, the doping element M includes one or a combination of more than one of cations Mn, Fe, Co, Ni, Al, Ga, Nb, Ta, Ce, Pr, Nd, Sm, Gd, Yb, and Y.

[0037] The doping element D may include one or a combination of more than one of the anions N, F, P, and S.

[0038] The molar content of the doping element M is less than or equal to 12% of the molar amount of the solid electrolyte by mole; the molar content of the doping element D is less than or equal to 5% of the molar amount of the solid electrolyte.

[0039] Further, Li and M, or Li, M, and D exist in a form including one or more of an oxide, fluoride, sulfide, nitrogen-containing compound, phosphate, and complex thereof at the grain boundary and the surface of the solid electrolyte.

[0040] Further, the lithium-lanthanum-zirconium composite oxide includes a garnet-type structure.

[0041] According to a second aspect of the present application, provided is a preparation method for the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to the first aspect of the present application. The flowchart of the preparation method is shown in FIG. 1. The method includes a co-precipitation method and a grain boundary doping method, the method including the steps of: [0042] S1, mixing aqueous solutions of lanthanum and zirconium compounds in a desired stoichiometric ratio to obtain a mixed material liquid; adding the mixed material liquid and an alkaline substance into a reactor for a precipitation reaction; performing suction filtration, washing, drying, and roasting on the obtained precipitate to obtain a lanthanum-zirconium oxide, in this step S1, impurity ions in the precipitate are removed by washing; and [0043] S2, mixing the lanthanum-zirconium oxide with liquid salts of doping elements M and Li under a stirring condition in one or more steps, drying and then performing once or twice heat treatments, and then performing once or twice heat calcinations to obtain the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte.

[0044] In a third aspect of the present application, provided is a preparation method for the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte according to the first aspect of the present application, which may employ the following steps: [0045] S1, mixing aqueous solutions of lanthanum and zirconium, and M or a part of M compound in a desired stoichiometric ratio to obtain a mixed material liquid; adding the mixed material liquid and an alkaline substance into a reactor for a precipitation reaction; performing suction filtration, washing, drying, and roasting on the obtained precipitate to obtain an M-containing lanthanum-zirconium oxide; and [0046] S2, mixing the M-containing lanthanum-zirconium oxide with a liquid salt of Li or a mixed liquid salt of the remaining doping element M and Li under a stirring condition in one or more steps, drying and then performing once or twice heat treatments, and then performing once or twice heat calcinations to obtain the grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte.

[0047] In the preparation method provided in the above second and third aspects, all or part of Li may be added to the M-containing lanthanum-zirconium oxide in the form of solid salt.

[0048] In the above-mentioned preparation methods, step S1 mainly involves a co-precipitation method, and step S2 mainly involves to a grain boundary doping method. Lithium-lanthanum-zirconium composite oxide solid electrolyte is prepared by the co-precipitation method and the grain boundary doping method, so that the doping element is located at the grain boundaries and surfaces of the lithium-lanthanum-zirconium composite oxide solid electrolyte, improving the distribution state of the doping elements at the grain boundary, reducing the number of grain boundaries, reducing the grain boundary resistance of the lithium-lanthanum-zirconium composite oxide, and improving the ion conductivity of the lithium-lanthanum-zirconium composite oxide solid electrolyte. This method is versatile and can meet the requirements of different solid electrolytes for doping elements.

[0049] The zirconium source in the mixed material liquid in step S1 includes one or a combination of more than one of zirconium oxychloride, zirconium oxynitrate, zirconium sulfate, zirconium acetate, and zirconium citrate; the lanthanum source includes one or a combination of more than one of lanthanum chloride, lanthanum nitrate, lanthanum sulfate, lanthanum acetate, and lanthanum citrate. The alkaline substance includes magnesium bicarbonate, urea, and at least one of hydroxide, carbonate, or bicarbonate of at least one element of ammonium, sodium, or potassium, preferably including at least one of sodium hydroxide, urea, aqueous ammonia, and ammonium bicarbonate.

[0050] In step S1, adding the mixed material liquid and the alkaline substance into the reactor for the precipitation reaction, the pH during the precipitation process is controlled in the range of 4.5-14, preferably 5-10; the endpoint pH of the precipitation is controlled at 8-13, preferably 9-11; the temperature is controlled at 0-120 C., preferably 10-80 C.

[0051] The liquid salt of the doping element M or Li includes one or a combination of more than one of nitrate, acetate, sulfate, citrate, and an amino acid salt molten salt or aqueous solution.

[0052] Doping element D is added in one or more of the steps S1 and S2; the doping element D is derived from one or a combination of more than one of nitrate, fluoride, phosphate, sulfate, and sulfide.

[0053] The roasting temperature in step S1 is 600-1000 C., preferably 700-900 C.; and the roasting time is 1-24 h, preferably 3-15 h.

[0054] The heat treatment temperature in step S2 is 200-750 C., preferably 400-600 C.; and the heat treatment time is 1-24 h, preferably 3-15 h. The drying temperature is 50-200 C., and the drying time is 1-24 h. The calcination temperature is 700-1100 C., preferably 800-950 C. The calcination time is 1-24 h, preferably 3-15 h. The morphology and ratio of Li and M at the grain boundary and surface can be controlled by controlling precipitation parameters, heat treatment, and calcination temperature, time, and atmosphere of the product. In order to meet the special requirements of different applications for different applications, it is necessary to adjust or change the type of doping elements and the microstructure of the electrolyte, so it is necessary to adopt different heat treatment systems, such as stepwise heat treatment, so that more doping elements enter the grain boundaries and surfaces more uniformly and stably, and water washing, water quenching and other treatments can also be performed from the two heat treatments. The lithium-lanthanum-zirconium composite oxide obtained above may also be subjected to two times of calcination so that the particle size and dispersibility thereof can be effectively controlled. After the calcination, ball milling, and surface treatment can be performed to avoid secondary sintering agglomeration.

[0055] In a fourth aspect of the present application, provided is use of the lithium-lanthanum-zirconium composite oxide solid electrolyte according to the first aspect of the present application in the fields such as all-solid lithium metal or lithium ion batteries, semi-solid lithium ion batteries, lithium air batteries. The lithium-lanthanum-zirconium composite oxide solid electrolyte of the embodiments of the present application can be used in fields such as solid lithium metal or lithium ion batteries, semi-solid lithium ion batteries, lithium air batteries, etc. resulting in higher energy density and better safety performance.

[0056] The grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte powder can be prepared into a ceramic by a casting method, a thermal method, etc. It can also be mixed with a polymer, or structurally designed to prepare a composite solid electrolyte with a layered structure that matches the electrode material better.

[0057] The present application is further described below by way of specific examples.

Comparative Example 1

[0058] According to the stoichiometric ratio, La(NO.sub.3).sub.3, ZrO(NO.sub.3).sub.2, and Mn(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M with water. Under a stirring condition, the mixed material liquid and 3.0 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 70.2, the endpoint pH was 11, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium-manganese oxide. Li.sub.2CO.sub.3 was mixed with the lanthanum-zirconium-manganese oxide evenly through ball milling and calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with Mn in the bulk phase, Li.sub.7La.sub.3Zr.sub.1.8Mn.sub.0.2O.sub.12. The ionic conductivity was measured to be 1.8910.sup.4 S/cm (25 C.).

Comparative Example 2

[0059] According to the stoichiometric ratio, La(NO.sub.3).sub.3, and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M with water. Under a stirring condition, the mixed material liquid and 3.0 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 70.2, the endpoint pH was 11, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. MnO.sub.2 and Li.sub.2CO.sub.3 were mixed with the lanthanum-zirconium oxide evenly through ball milling and calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with Mn at the bulk phase, Li.sub.7La.sub.3Zr.sub.1.8Mn.sub.0.2O.sub.12. The ionic conductivity was measured to be 1.5610.sup.4 S/cm (25 C.).

Example 1

[0060] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M with water. Under a stirring condition, the mixed material liquid and 3.0 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 70.2, the endpoint pH was 11, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Mn(NO.sub.3).sub.2 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Mn and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 450 C. for 10 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Mn and Li at the grain boundary and the surface, Li.sub.7La.sub.3Zr.sub.1.8Mn.sub.0.2O.sub.12. Its ionic conductivity was measured to be 6.0310.sup.4 S/cm (25 C.).

Example 2

[0061] According to the stoichiometric ratio, La.sub.2(SO.sub.4).sub.3 and Zr(SO.sub.4).sub.2 were prepared into a mixed solution with a total cation concentration of 0.5 M. Under a stirring condition, the mixed material liquid and 3.0 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 90.2, the endpoint pH was 10, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 850 C. for 8.5 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Al(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Al and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 450 C. for 12 h, and finally calcined at 850 C. for 10 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide and sulfide of Al and Li at the grain boundary and the surface, L.sub.16.25La.sub.3Zr.sub.2Al.sub.0.25O.sub.11.4S.sub.0.6. Its ionic conductivity was measured to be 7.0110.sup.4 S/cm (25 C.).

Example 3

[0062] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3.0 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was 5-9, the endpoint pH was 11, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 600 C. for 48 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Fe(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Fe and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 200 C. for 12 h, and finally calcined at 860 C. for 9.5 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Fe at the grain boundary and the surface, Li.sub.6.7La.sub.3Zr.sub.2Fe.sub.0.1O.sub.12. Its ionic conductivity was measured to be 4.2510.sup.4 S/cm (25 C.).

Example 4

[0063] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 3.0 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 80.2, the endpoint pH was 9.5, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Co(NO.sub.3).sub.2 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Co and Li. The mixture was dried at 80 C. for 18 h, then subjected to heat treatment at 550 C. for 8 h, then calcined at 800 C. for 8 h, and finally calcined at 950 C. for 7 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Co at the grain boundary and the surface, Li.sub.7La.sub.3Zr.sub.1.5Co.sub.0.5O.sub.12. Its ionic conductivity was measured to be 6.8610.sup.4 S/cm (25 C.).

Example 5

[0064] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 4.0 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was 9-12, the endpoint pH of the precipitation was 9, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 900 C. for 8 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ni(CH.sub.3COO).sub.2 and CH.sub.3COOLi liquid salts of Ni and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 680 C. for 6.5 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ni at the grain boundary and the surface, Li.sub.7La.sub.3Zr.sub.1.8Ni.sub.0.4O.sub.12. Its ionic conductivity was measured to be 5.3610.sup.4 S/cm (25 C.).

Example 6

[0065] According to the stoichiometric ratio, La(CH.sub.3COO).sub.3 and Zr(CH.sub.3COO).sub.4 were prepared into a mixed solution with a total cation concentration of 0.5 M. Under a stirring condition, the mixed material liquid and 3.5 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 80.2, the endpoint pH was 11, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ga(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ga and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 600 C. for 6 h, and finally calcined at 920 C. for 8.5 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ga at the grain boundary and the surface, Li.sub.6.4La.sub.3Zr.sub.2Ga.sub.0.2O.sub.12. Its ionic conductivity was measured to be 1.1410.sup.3 S/cm (25 C.).

Example 7

[0066] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M sodium hydroxide solution were added to a reactor at an even speed. The pH of the precipitation process was 10-14, the endpoint pH was 10, and the temperature was controlled to be 60 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 750 C. for 10 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with NbO(NO.sub.3).sub.3, LiNO.sub.3, and NH.sub.4F liquid salts stepwise in the stoichiometric ratio of the doped Ni and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 600 C. for 6 h, and finally calcined at 940 C. for 8 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide and fluoride of Li and Nb at the grain boundary and the surface, Li.sub.6.3La.sub.3Zr.sub.1.4Nb.sub.0.7O.sub.11.75F.sub.0.5. Its ionic conductivity was measured to be 9.6510.sup.4 S/cm (25 C.).

Example 8

[0067] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M sodium hydroxide solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 80.2, the endpoint pH was 9.5, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 1000 C. for 1 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ce(NO.sub.3).sub.3, LiNO.sub.3, and (NH.sub.4).sub.3PO.sub.4 liquid salts stepwise in the stoichiometric ratio of the doped Ce and Li. The mixture was dried at 100 C. for 5 h, then subjected to heat treatment at 750 C. for 1 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide and phosphate of Li and Ce at the grain boundary and the surface, Li.sub.6.8La.sub.2.8Zr.sub.2Ce.sub.0.2O.sub.10.5P. Its ionic conductivity was measured to be 5.0810.sup.4 S/cm (25 C.).

Example 9

[0068] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3.05 M sodium hydroxide solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 80.2, the endpoint pH of the precipitation was 13, and the temperature was controlled to be 0 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 750 C. for 10 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Pr(NO.sub.3).sub.3.6H.sub.2O and LiNO.sub.3 liquid salts in the stoichiometric ratio of doped Pr and Li. The mixture was dried at 50 C. for 24 h, then subjected to heat treatment at 200 C. for 12 h, and another heat treatment at 500 C. for 8.5 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Pr at the grain boundary and the surface, Li.sub.7La.sub.2.6Zr.sub.2Pr.sub.0.4O.sub.12. Its ionic conductivity was measured to be 5.5610.sup.4 S/cm (25 C.).

Example 10

[0069] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M sodium hydroxide solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 90.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 80 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 850 C. for 8.5 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Nd(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Nd and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 530 C. for 8 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ni at the grain boundary and the surface, Li.sub.7La.sub.2.2Zr.sub.2Nd.sub.0.8O.sub.12. Its ionic conductivity was measured to be 6.5910.sup.4 S/cm (25 C.).

Example 11

[0070] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M sodium hydroxide solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 90.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 10 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 650 C. for 3 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Sm(NO.sub.3).sub.3.Math.6H.sub.2O and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Sm and Li. The mixture was dried at 100 C. for 6 h, then subjected to heat treatment at 500 C. for 8.5 h, then calcined at 800 C. for 8 h, and calcined again at 950 C. for 4 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Sm at the grain boundary and the surface, Li.sub.7La.sub.2.5Zr.sub.2Sm.sub.0.5O.sub.12. Its ionic conductivity was measured to be 5.0310.sup.4 S/cm (25 C.).

Example 12

[0071] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M sodium hydroxide solution were added to a reactor at an even speed. The pH of the precipitation process was 6-10, the endpoint pH of the precipitation was 11, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 750 C. for 10 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Gd(NO.sub.3).sub.3.Math.6H.sub.2O and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Gd and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 460 C. for 9 h, and calcined at 800 C. for 15 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide and nitrogen-containing compound of Li and Gd at the grain boundary and the surface, Li.sub.7La.sub.2.5Zr.sub.2Gd.sub.0.5O.sub.11.91N.sub.0.06. Its ionic conductivity was measured to be 8.4210.sup.4 S/cm (25 C.).

Example 13

[0072] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 3 M urea solution were added to a reactor. The temperature of the reaction was controlled to be 120 C. to carry out the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 850 C. for 8.5 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Yb(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Yb and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 500 C. for 8.5 h, and finally calcined at 800 C. for 15 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Yb at the grain boundary and the surface, Li.sub.7La.sub.2Zr.sub.2YbO.sub.12. Its ionic conductivity was measured to be 6.8910.sup.4 S/cm (25 C.).

Example 14

[0073] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor. The pH of the precipitation process was controlled to be 80.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with TaO(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ta and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 550 C. for 8 h, and finally calcined at 700 C. for 24 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ta at the grain boundary and the surface, Li.sub.6.5La.sub.3Zr.sub.1.5Ta.sub.0.5O.sub.12. Its ionic conductivity was measured to be 5.4810.sup.4 S/cm (25 C.).

Example 15

[0074] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor. The pH of the precipitation process was controlled to be 70.2, the endpoint pH of the precipitation was 9.5, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Y(NO.sub.3).sub.3.Math.6H.sub.2O and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Y and Li. The mixture was dried at 150 C. for 8 h, then subjected to heat treatment at 530 C. for 8 h, and finally calcined at 870 C. for 9.5 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Y at the grain boundary and the surface, Li.sub.7La.sub.1.5Zr.sub.2Y.sub.1.5O.sub.12. Its ionic conductivity was measured to be 9.1210.sup.4 S/cm (25 C.).

Example 16

[0075] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 80.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with TaO(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ta and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 550 C. for 8 h, and finally calcined at 800 C. for 15 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ta at the grain boundary and the surface, Li.sub.6.4La.sub.3Zr.sub.1.6Ta.sub.0.6O.sub.12. Its ionic conductivity was measured to be 7.7510.sup.4 S/cm (25 C.).

Example 17

[0076] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 100.2, the endpoint pH of the precipitation was 10.5, and the temperature was controlled to be 50 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 700 C. for 15 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Cu(NO.sub.3).sub.2 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Cu and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 400 C. for 15 h, and finally calcined at 930 C. for 8.5 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Cu at the grain boundary and the surface, Li.sub.7La.sub.3Zr.sub.1.2Cu.sub.1.6O.sub.12. Its ionic conductivity was measured to be 6.8310.sup.4 S/cm (25 C.).

Example 18

[0077] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 80.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with TaO(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ta and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 550 C. for 9 h, and finally calcined at 950 C. for 8 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ta at the grain boundary and the surface, Li.sub.6La.sub.3ZrTaO.sub.12. Its ionic conductivity was measured to be 8.3510.sup.4 S/cm (25 C.).

Example 19

[0078] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 0.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 4.5-9, the endpoint pH of the precipitation was 11, and the temperature was controlled to be 60 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 700 C. for 15 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with TaO(NO.sub.3).sub.3, NbO(NO.sub.3).sub.3, and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ta, Nb, and Li. The mixture was dried at 120 C. for 10 h, then subjected to heat treatment at 580 C. for 7.5 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li, Nb, and Ta at the grain boundary and the surface, Li.sub.6.6La.sub.3Zr.sub.1.6Ta.sub.0.2Nb.sub.0.2O.sub.12. Its ionic conductivity was measured to be 9.8910.sup.4 S/cm (25 C.).

Example 20

[0079] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution of La.sup.3+ and Zr.sup.4+ with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor. The pH of the precipitation process was controlled to be 80.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with TaO(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ta and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 550 C. for 8 h, and finally calcined at 1100 C. for 1 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ta at the grain boundary and the surface, Li.sub.6.15La.sub.3Zr.sub.1.85Ta.sub.0.85O.sub.12. Its ionic conductivity was measured to be 5.0910.sup.1 S/cm (25 C.).

Example 21

[0080] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 0.5 M. Under a stirring condition, the mixed material liquid and 4 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 60.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 850 C. for 5 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ga(NO.sub.3).sub.3, Al(NO.sub.3).sub.3, and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ga, Al, and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 600 C. for 6 h, and finally calcined at 850 C. for 10 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li, Al, and Ga at the grain boundary and the surface, Li.sub.6.1La.sub.3Zr.sub.2Al.sub.0.1Ga.sub.0.2O.sub.12. Its ionic conductivity was measured to be 3.1210.sup.3 S/cm (25 C.).

Example 22

[0081] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 60.2, the endpoint pH of the precipitation was 12, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 750 C. for 10 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with TaO(NO.sub.3).sub.3, LiNO.sub.3, and NH.sub.4F liquid salts in the stoichiometric ratio of the doped Ta and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 550 C. for 8 h, and finally calcined at 830 C. for 13 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide and fluoride of Li and Ta at the grain boundary and the surface, Li.sub.6.5La.sub.3Zr.sub.1.5Ta.sub.0.5O.sub.11.75F.sub.0.5. Its ionic conductivity was measured to be 8.4010.sup.4 S/cm (25 C.).

Example 23

[0082] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 50.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 750 C. for 10 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with TaO(NO.sub.3).sub.3, NbO(NO.sub.3).sub.3, LiNO.sub.3, and NH.sub.4F liquid salts in the stoichiometric ratio of the doped Ta, Nb, and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 500 C. for 8.5 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide and fluoride of Li, Ta, and Nb at the grain boundary and the surface, Li.sub.6.6La.sub.3Zr.sub.1.6Ta.sub.0.2Nb.sub.0.2O.sub.11.95F.sub.0.1. Its ionic conductivity was measured to be 1.3210.sup.3 S/cm (25 C.).

Example 24

[0083] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor. The pH of the precipitation process was controlled to be 80.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with TaO(NO.sub.3).sub.3 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ta and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 550 C. for 9 h, and finally calcined at 850 C. for 11 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ta at the grain boundary and the surface, Li.sub.6.2La.sub.3Zr.sub.1.8Ta.sub.0.8O.sub.12. Its ionic conductivity was measured to be 8.8910.sup.4 S/cm (25 C.).

Example 25

[0084] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 3 M mixed solution of ammonium bicarbonate and aqueous ammonia were added to a reactor. The pH of the precipitation process was controlled to be 80.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 850 C. for 8.5 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Eu(NO.sub.3).sub.2 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Eu and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 570 C. for 7.5 h, and finally calcined at 820 C. for 13 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Eu at the grain boundary and the surface, Li.sub.7La.sub.3Zr.sub.1.1Eu.sub.1.8O.sub.12. Its ionic conductivity was measured to be 6.8810.sup.4 S/cm (25 C.).

Example 26

[0085] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor. The pH of the precipitation process was controlled to be 9.50.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 45 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ti(NO.sub.3).sub.4 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ti and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 460 C. for 9.5 h, and finally calcined at 860 C. for 10.5 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ti at the grain boundary and the surface, Li.sub.7La.sub.3Zr.sub.1.9Ti.sub.0.1O.sub.12. Its ionic conductivity was measured to be 5.8110.sup.4 S/cm (25 C.).

Example 27

[0086] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 5.5-11, the endpoint pH of the precipitation was 12, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ca(NO.sub.3).sub.2 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ca and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 410 C. for 13 h, and finally calcined at 840 C. for 12 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ca at the grain boundary and the surface, Li.sub.7La.sub.1.8Zr.sub.2Ca.sub.1.8O.sub.12. Its ionic conductivity was measured to be 6.1210.sup.4 S/cm (25 C.).

Example 28

[0087] According to the stoichiometric ratio, La.sub.2(SO.sub.4).sub.3 and Zr(SO.sub.4).sub.2 were prepared into a mixed solution with a total cation concentration of 0.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 70.2, the endpoint pH of the precipitation was 11, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 850 C. for 8.5 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ga(NO.sub.3).sub.3, Al(NO.sub.3).sub.3, and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ga, Al, and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 600 C. for 6 h, and then calcined at 850 C. for 18 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide and sulfide of Li, Al and Ga at the grain boundary and the surface, Li.sub.6.1La.sub.3Zr.sub.2Al.sub.0.1Ga.sub.0.2O.sub.11S. Its ionic conductivity was measured to be 4.3210.sup.3 S/cm (25 C.).

Example 29

[0088] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor. The pH of the precipitation process was controlled to be 9.50.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 45 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ga(NO.sub.3).sub.3, LiNO.sub.3, and (NH.sub.4).sub.3PO.sub.4 liquid salts in the stoichiometric ratio of the doped Ga and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 450 C. for 12 h, and finally calcined at 800 C. for 15 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide and phosphate of Li and Ga at the grain boundary and the surface, Li.sub.4La.sub.3Zr.sub.2GaO.sub.10.5P. Its ionic conductivity was measured to be 9.9110.sup.4 S/cm (25 C.).

Example 30

[0089] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 8.50.2, the endpoint pH of the precipitation was 12, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 750 C. for 10 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ga(NO.sub.3).sub.3, TaO(NO.sub.3).sub.3, Ba(NO.sub.3).sub.2, and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ga, Ba, Ta, and Li. The mixture was dried at 50 C. for 24 h, then subjected to heat treatment at 480 C. for 12 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li, Ga, Ba, and Ta at the grain boundary and the surface, Li.sub.6.4Ga.sub.0.1La.sub.3Zr.sub.1.55Ta.sub.0.4Ba.sub.0.05O.sub.12. Its ionic conductivity was measured to be 8.3610.sup.4 S/cm (25 C.).

Example 31

[0090] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3.05 M sodium hydroxide solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 80.2, the endpoint pH of the precipitation was 12, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 750 C. for 10 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Al(NO.sub.3), RbNO.sub.3, and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Al, Rb, and Li. The mixture was dried at 50 C. for 24 h, then subjected to heat treatment at 400 C. for 15 h, and finally calcined at 900 C. for 9 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Rb at the grain boundary and the surface, Li.sub.6.1La.sub.2.1Zr.sub.2Al.sub.0.3Rb.sub.2.7O.sub.12. Its ionic conductivity was measured to be 7.9610.sup.4 S/cm (25 C.).

Example 32

[0091] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.5 M. Under a stirring condition, the mixed material liquid and 3.05 M sodium hydroxide solution were added to a reactor at an even speed. The pH of the precipitation process was controlled to be 8.50.2, the endpoint pH of the precipitation was 12, and the temperature was controlled to be 45 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 750 C. for 10 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ge(NO.sub.3).sub.4 and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ge and Li. The mixture was dried at 50 C. for 24 h, then subjected to heat treatment at 400 C. for 14 h and another heat treatment at 700 C. for 16 h, finally calcined at 900 C. for 9 h, and calcined again at 950 C. for 8 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li and Ge at the grain boundary and the surface, Li.sub.7La.sub.3Zr.sub.1.7Ge.sub.0.3O.sub.12. Its ionic conductivity was measured to be 6.5610.sup.4 S/cm (25 C.).

Example 33

[0092] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor. The pH of the precipitation process was controlled to be 6.50.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 45 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Al(NO.sub.3).sub.3, TaO(NO.sub.3).sub.3, and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Al, Ta, and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 600 C. for 6 h, and finally calcined at 850 C. for 11 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li, Al, and Ta at the grain boundary and the surface, Li.sub.6.2Al.sub.0.2La.sub.3Zr.sub.1.8Ta.sub.0.2O.sub.12. Its ionic conductivity was measured to be 9.2110.sup.4 S/cm (25 C.).

Example 34

[0093] According to the stoichiometric ratio, La(NO.sub.3).sub.3 and ZrO(NO.sub.3).sub.2 were prepared into a mixed solution with a total cation concentration of 1.0 M. Under a stirring condition, the mixed material liquid and 3 M aqueous ammonia solution were added to a reactor. The pH of the precipitation process was controlled to be 9.50.2, the endpoint pH of the precipitation was 10, and the temperature was controlled to be 40 C. for the precipitation reaction. The precipitate obtained was filtered, washed, and dried, and the dried product was roasted at 800 C. for 9 h to obtain a lanthanum-zirconium oxide. The lanthanum-zirconium oxide was mixed with Ga(NO.sub.3).sub.3, RbNO.sub.3, and LiNO.sub.3 liquid salts in the stoichiometric ratio of the doped Ga, Rb, and Li. The mixture was dried at 100 C. for 12 h, then subjected to heat treatment at 550 C. for 8.5 h, and finally calcined at 860 C. for 10.5 h to obtain a lithium-lanthanum-zirconium composite oxide solid electrolyte doped with the oxide of Li, Ga, and Rb at the grain boundary and the surface, Li.sub.6.5Ga.sub.0.2La.sub.2.95Rb.sub.0.05Zr.sub.2O.sub.12. Its ionic conductivity was measured to be 2.0110.sup.3 S/cm (25 C.).

[0094] As can be seen from the above results, the lithium-lanthanum-zirconium composite oxide solid-state electrolyte obtained by the preparation method of the examples of the present application has significantly improved ionic conductivity compared to the oxides prepared in the comparative examples.

[0095] The present application relates to a grain boundary- and surface-doped lithium-lanthanum-zirconium composite oxide solid electrolyte, a preparation method therefor, and an application thereof. Part of doping elements are step-doped at the grain boundary and the surface of the lithium-lanthanum-zirconium composite oxide solid electrolyte to improve the distribution state of the doping elements at the grain boundaries, reduce the number of grain boundaries, lower the grain boundary resistance of the lithium-lanthanum-zirconium composite oxide, and improve the ionic conductivity of lithium-lanthanum-zirconium composite oxide solid state electrolyte. The technical solution of the present application provides a universally applicable grain boundary doping method, realizing an efficient and low-cost reduction of the grain boundary resistance of lithium-lanthanum-zirconium composite oxides, thereby enhancing the conductivity of ions, which can satisfy the demand for doping elements in different solid-state electrolytes and is suitable for scale-up applications.

[0096] It should be understood that the above specific embodiments of the present application are merely for exemplary illustration or explanation of the principles of the present application, and do not constitute a limitation of the present application. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present application shall be included in the scope of the present application. Furthermore, the appended claims of the present application are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.